Abstract: In this paper, a method for structure recognition based on multi-frequency eddy current signal processing is put forward, in which low-frequency signals in absolute channel obtained from multi-frequency eddy current instrument are adopted, and several pairs of signals are obtained by revolving transformation, and that pair with least amplitude is determined. The trend of the whole signal is got by median filtering and is used to cancel the sway and stand out the structure signals. And then, the structure centers and their number are determined by the amplitude threshold and the least interval. At last, these structures are recognized and shown based on the characters of bend tubes and supports. The effectiveness of this algorithm is proven by recognition of multiple groups of data from several NPP.